In particular, this code here looks suspect:

            if vx < limits[0]: row = r[1][0]
            elif vx >= limits[1]: row = r[1][0] #row is inclusive to right            
            if vy <= limits[2]: col = r[1][1]#col is inclusive toward bottom
            elif vy > limits[3]: col = r[1][1]
            if vz < limits[4]: depth = r[1][2]
            elif vz >= limits[5]: depth = r[1][2]#depth is inclusive toward front            

...just taking the X test case, it looks like if x < this_region_minX, then the row is set to this one, otherwise if x >= this_region_maxX, then the row is also set to this one.  The problem is, one or the other of those cases will always be true - ne?  Or am I missing some subtlety of what you're doing there?

Cinema4D Plugins (Home of Riptide, Riptide Pro, Undertow, Morph Mill, KyamaSlide and I/Ogre plugins) Poser products Freelance Modelling, Poser Rigging, UV-mapping work for hire.